南极半岛海洋气候区的土壤Ⅶ. 矿物学特性

南极海洋气候区岩石风化和土壤形成过程中有明显的原生矿物蚀变作用和自生矿物成矿作用。本文以粗骨寒冻灰化土和石灰性扰动冻土两种有代表性的土壤类型为例,阐述了本区土壤矿物学特征。指出铝氧化物、绿泥石、碳酸盐是本区玄武岩类风化物质上发育土壤中的主要自生矿物类型,蒙脱石、特别是绿泥-蒙脱石混层矿物是南极海洋气候区土壤粘粒部分的特征矿物。不同土壤由于成土环境、成土过程、成土历史的差异,其土壤物质的矿物学组成、含量、形态、分布具有明显不同。土壤发生性铁氧化物与成土作用和土壤过程密切相关,其矿物类型、含量、形态特征、分布模式在不同的土壤中明显不同,是表征土壤发育程度与剖面形态表达的有效指标。     

Pedogenic chlorites in podzolic soils with different intensities of hydromorphism: Origin,properties, and conditions of their formation

Minerals of the pedogenic chlorite group were studied in the clay fractions isolated from the mineral horizons of podzolic and gleyic peat-podzolic soils. In the AE and E horizons of the podzolic soil, pedogenic chlorites are thought to develop from vermiculite, whereas in the E horizon of the gleyic peat-podzolic soil, they can be formed from smectite minerals. For estimating the degree of chloritization (the degree of filling of the interlayer space of 2: 1 minerals with Al hydroxides), a numerical criterion was is proposed. The difference between the values of this criterion before and after the treatment of the preparations with NH₄F indicated that the degree of chloritization in the pedogenic chlorites decreases in the following sequence: the E horizon of the podzolic soil > the AE horizon of the podzolic soil > the E horizon of the gleyic peat-podzolic soil. Another numerical criterion was proposed to estimate the degree of polymerization of Al-hydroxy complexes in pedogenic chlorites. This criterion was based on the thermal stability of soil chlorites and represented the temperature at which an increase in the intensity of the 1.0-nm peak after heating the K-saturated preparations exceeds 50% of its initial value. According to this criterion, the degree of polymerization of the Al-hydroxy interlayers in pedogenic chlorites decreases in the following sequence: the E horizon of the podzolic soil > the E horizon of the gleyic peat-podzolic soil ≥ the AE horizon of the podzolic soil. The distinct interrelation between the soil properties and the degrees of chloritization and polymerization of the Al-hydroxy interlayers attests to the modern origin of the pedogenic chlorites.     

Soil system and pedogenic processes: Self-organization, time scales, and environmental significance

The essence of pedogenesis, as a synergetic process, consists in generation, selection, accumulation and differentiation of the solids produced in the course of bio-abiotic processes functioning within a soil body. Soil formation in the broad sense is the result of synergetic processes of self-organization of an in situ soil system during its functioning in time and space. Soil formation, sensu stricto, is the transformation of the solid-phase lithomatrix (parent material) of the soil system into the pedomatrix (soil body, soil mantle). Pedogenesis is perceived as an integration of specific pedogenic processes (SPP); each of them characterized by a definite set of solid-phase pedogenic features. Each soil body is formed by a combination of some SPP. The whole set of SPP may be grouped in accordance with their essence, characteristic times (rates) and reversibility-irreversibility. In terms of characteristic times (rates) they may be arranged in three main groups: rapid (10^1–2 years), medium-rate (10^3–4 years), and slow (10^5–6 years). Soil system functioning and soil formation are intimately linked but fundamentally different processes: the former is infinite in time, if not interrupted by external factors; the latter, as any self-organization process, is finite in time and tends to reach a steady state. The theoretical grouping of the pedogenic processes according to their essence and self-termination or quasi-equilibrium is proposed. All the diagnostic soil horizons (as defined in WRB) are perceived as more or less stable and “mature” degrees of soil self-development. They may be separated into favorable and unfavorable with respect to their suitability for biota. Favorable conditions are generally common in 12 out of 39 diagnostic horizons and properties (32%). They are mainly influenced by biotic fluxes and cycles, which are comparable to, or exceed, abiotic fluxes and cycles in their strength and capacity. In this case, biota transforms and improves the environment rather than adapts to it. Unfavorable conditions are more common in 27 out of 39 diagnostic horizons and properties (68%). They are influenced by the mutual action both of biotic and abiotic fluxes and cycles. In this case, biota adapts to the environment rather than improves it.     

Biogenic and chemogenic calcium accumulations in Mollisols developed from loess in Argentina pampas

The morphology of pedogenic calcium accumulations, their distribution in the soil profile, and the mechanisms of their formation in Mollisols of Argentina pampas were studied in the southeast of the Buenos Aires province. The chemogenic collomorphic calcareous films and tubes and the biogenic (cyanobacterial) gypsum framboidal structures (spherulites) were detected with the use of electron microscopy. Two mechanisms of the formation of framboidal gypsum were identified: (a) the formation of crystalline gypsum crusts around less soluble minerals (calcite) by spherical colonies of cyanobacteria and (b) the inheritance of the spherical shape of gypsum pedofeatures from the framboidal pyrite concretions accumulated in marine deposits and subjected to decomposition by sulfate-reducing bacteria. It is probable that the cyanobacterial gypsum accumulations are only formed in the studied soils during the dry season and are dissolved during the wet season.     

土壤铁矿物的生物-非生物转化过程及其界面重金属反应机制的研究进展

铁矿物作为土壤的重要组成成分,一般可通过吸附、络合和共沉淀等方式影响重金属的生物有效性和毒性.此外,土壤中有机物的存在会影响铁矿物的转化,导致转化产物的结构和表面特性发生改变,进一步影响重金属的环境行为.本文从铁矿物、有机质和重金属等要素入手,综述了反应pH、温度、亚铁和微生物等因素影响下土壤铁矿物非生物和生物转化过程...     

The impact of redox conditions on the rare earth element signature of redoximorphic features in a soil sequence developed from limestone

Redox processes, which are widespread in soils, need to be quantified for an improved comprehension of the dynamics of Fe- and Mn-oxides and their associated trace elements. The classical methodology used to study these redox processes generally relies on the quantification of all mineral species in the various pedological features that can be related to different redox stages. However, this approach usually encounters the difficulty of precisely quantifying the different forms of poorly crystallised Fe- and Mn-oxides.In this study, we use the signature of rare earth elements (REEs) to visualise and, eventually, quantify the importance of redox processes in soils. Our approach relies on that developed by Laveuf et al. (2008) and the idea that the relative contribution to the mobilisation of REEs that is made by the primary minerals reactive to redox conditions depends on the following factors: (i) their initial proportion in the different pedological features that can be related to various redox processes, (ii) their relative mobilisation during the redox process in question, and (iii) their initial REE signatures.The catena studied is characterised by two stages of redox conditions: the first is related to the formation and subsequent dissolution of Fe–Mn concretions, and the second is related to the bleaching of the soil matrix due to morphological degradation. In this soil, the main minerals reactive to redox conditions are Mn-oxides, ferrihydrite, goethite and (fluor)apatite. The results indicate that the primary redox conditions can be characterised by a positive Ce anomaly on the REE pattern, which has been attributed to a preferential immobilisation of this element, due to its association with Mn-oxides. The results also indicate that the secondary redox conditions can be characterised by depletion in medium REEs (MREEs) in the REE pattern, which has been attributed to a preferential release of these elements during the dissolution of (fluor)apatite and, to a lesser extent, of ferrihydrite.These results emphasise the potential of REE signatures of the visualisation of the various redox processes that have been active in a soil. Additionally, REE signatures are a proxy of the frequency and intensity of the redox conditions.     

土壤微生物—腐殖质—矿物间的胞外电子传递机制研究进展

微生物胞外电子传递是地球表层系统元素循环与能量交换的重要驱动力。近年来,以微生物—腐殖质—矿物之间电子转移为核心的生物地球化学过程得到重视,拓展了以带电的土壤胶体与离子之间的相互作用为重心的土壤界面过程的内涵,成为地球表层系统物质间相互作用新的关注点,启示我们从化学与生物两个角度重新认识地球表层系统过程。本文从微生物、腐殖质和矿物等要素入手,综述了其地球化学角色与功能,讨论了它们之间的相互关系以及胞外电子传递的途径与方式;从热力学的角度探讨了胞外电子传递过程的能量变化,从动力学的角度探讨了胞外电子传递的传质与速率;介绍了若干胞外电子传递的研究方法;并提出了今后需要重点关注的重要科学问题。     

Andosol to Luvisol evolution in Central Mexico: timing, mechanisms and environmental setting

Surface and buried Andosols and buried Luvisols of the Nevado de Toluca Late Quaternary tephra-paleosol sequence (Central Mexico) were studied to show whether these soils present an evolutionary sequence and to determine the pedogenic mechanisms and environmental factors involved in the evolutionary process. Micromorphological observations and mineralogical composition of fine sand and clay fractions were used to detect type and succession of soil-forming process. Some of the buried Andosols, defined as “intergrade” Andosols, have a predominantly blocky structure, humus-depleted areas, redoximorphic features and thin clay coatings in Ah horizons. Clay fractions of buried Andosols contain halloysite besides amorphous components, whereas in modern Andosols, allophane is dominant. Luvisols have micro-areas with granular structure and abundant phytoliths in the groundmass of Bt horizons assumed to be the relict Andosol features. Luvisol clay fractions are dominated by halloysite and kaolinite. Primary minerals show micromorphological weathering features in all studied soils being stronger in Luvisols; however, even in Luvisols, sand fractions consist mostly of unstable volcanic silicates. We hypothesise that the studied profiles form an evolutionary sequence: Andosols–“intergrade” Andosols–Luvisols; the soil transformation is supposed to be linked to progressive crystallisation of 1:1 clay minerals. Comparing the Nevado de Toluca paleosol properties with the existing data on volcanic soil climo- and chronesequences and assessing the regional paleopedological and lacustrine records of Quaternary paleoclimates, we concluded that wet/dry climatic oscillations took place during the formation of the studied paleosols. Rapid crystallisation of 1:1 minerals occurred during dry phases, which speeded up the Andosol to Luvisol transformation and made it independent from the primary mineral weathering status. The Andosol to Luvisol transformation accelerated by climatic fluctuations is thought to be a common soil evolutionary pathway in the subtropical and tropical regions of recent volcanism, which suffered contrasting precipitation oscillations in the Quaternary.     

Soils on hard rocks in the northwest of Russia: Chemical and mineralogical properties,genesis, and classification problems

Soil formation on hard rocks—nepheline syenite, amphibolite, metamorphized gabbro diabase, and their derivatives—was studied in the mountainous tundra and in the northern and middle taiga zones of the Kola Peninsula and Karelia (in the Kivach Reserve). It was found that the soils developing from these rocks could be classified into three groups: (1) petrozems with the O-M profile (the most common variant), (2) podzols and podzolized podburs on the substrates with an admixture of morainic derivatives of acid rocks, and (3) shallow (<5–10 cm) pebbly soils on the substrates without an admixture of allochthonous material (the rarest variant). In soils of the third group, the pedogenic alteration of the mineral matrix does not result in the appearance of phyllosilicates in the fine fractions if these phyllosilicates are initially absent in the rock. In these soils, the protion of the organic matter, and binding of iron released from the weathered silicate minerals into iron-organic complexes) are virtually undifferentiated by the separate soil horizons because of the very low thickness of the soil profiles. These soils have the Oao-BHFao-M profile; it is suggested that they can be classified as leptic podburs. An admixture of morainic material containing phyllosilicate minerals favors a more pronounced differentiation of the modern pedogenic processes by separate soil horizons even in the case of shallow soil profiles; the intense transformation of phyllosilicates takes place in the soils.     

Choosing models for soil chronofunctions and fitting them to data

The effectiveness and utility of soil chronofunctions is examined in the light of existing pedogenic theory. Statistical treatments applied in chronofunction research are reviewed, including linear transformations of raw data, which may improve the utility of the chronofunction. We advocate using a particular statistical model only if it can be justified based on our current understanding of the functioning of the pedologic system. We emphasize the potential difficulties of using linear chronofunction methods; simple linear and logarithmic functions are not always the best option for chronofunctions. Hyperbolic, polynomial or nonlinear functions might improve not only the fit of the chronofunction but also advance our understanding of the pedologic system. When the chronofunction explaining the most variance is not best suited to a process-based understanding of pedogenic theory, other functions with slightly smaller r² values that have been judged suitable by a priori reasoning or theory might better reflect the functioning of the pedologic system. We justify limited extrapolation of some chronofunctions to time zero and discuss how this can be useful in the identification of pedogenic thresholds and ‘step functions’. Interpretation of the Y-intercept of chronofunctions can, at times, aid our understanding of the soil system near time zero and be useful in the identification of the existence and timing of thresholds.     

Age and Some Genetic Characteristics of Vertisols in China

The ages of organic matter of some dark-colored horizons and calcareous concretions in some Vertisols from tropical,subtropical and warm-temperate zones of China were studied using radiocarbon dating method.The relationship between soil age and genesis of Vertisols was also expounded based on the study of their genetic characteristics and micromorphological features.The results show that although Vertisols have developed for a relatively long time,their weathering and soil forming process are weak and young with little horizonation.This is closely related to their special grochemical soil forming environment.Low-lying terrain,heavy texture,clay minerals dominated by montmorillonites and alternative drying-wetting climate give rise to the vertic features expressed in intense swelling-shrinking and cracking-closing in soils.As a result,the soil development and soil leaching process are resisted,and the climatic effect on the horizonation is impeded.Moreover,pedoturbation eliminates the horizonation in the upper part of soil profile,and postpones their evolution into zonal soils.So vertisols show certain pedogenic inertia and stay at relatively young developmental stage.Therefore,Vertisols are intrazonal soils dominated by local soil forming factors such as the relief and parent materials.     

海南岛北部玄武岩区土壤母质均一性及相对年龄判定

【目的】时间序列法是定量研究土壤发生过程、演变速率及其变化阈值的重要手段,构建可靠的土壤时间序列需对土壤母质均一性和相对年龄进行判定。【方法】以海南岛北部不同喷发期玄武岩发育土壤所构成的成土时间序列（0.09、0.146、0.64、1.12、1.81、2.30 Ma B. P.）为对象,利用各种土壤属性参数（包括剖面形态、颗粒组成、稳定元素含量、风化发育指数和元素变化率等）对该时间序列母质均一性和土壤相对年龄进行判定。【结果】各剖面颜色、质地、结构等形态总体呈均一、渐变的特征,去除黏粒后的粗粉粒含量、稳定元素Ti/Zr比值在剖面内和剖面间变化均较小,表明时间序列土壤的起源母质相同。随着成土年龄的增加,黏粒含量和剖面发育指数呈线性增加的趋势,土壤风化强度指标（B指数、CIW指数、CIA指数和ba值）服从对数函数变化规律,在土壤相对年龄的判定中具有较好的指示意义。【结论】研究区土壤母质来源相同,土壤相对年龄可通过相关土壤属性体现出来,为定量研究土壤发生阈值奠定了基础。     

Mineral magnetic properties of a weathering sequence of soils derived from basalt in Eastern China

The magnetic properties and magnetic mineralogy of a weathering sequence of soils developed on basalt parent material from eastern China, were studied by rock magnetism, X-ray diffraction and soil chemical analyses to establish the connection between mineral magnetic properties and pedogenic development in a subtropical region. The magnetic susceptibility of soils formed on basalt varied greatly and did not increase with the degree of pedogenic development. The frequency-dependent susceptibility (χfd) values of soils ranged from 1.0 to 11.1% and increased with the pedogenic development. Highly significant linear relationship was found between the frequency-dependent susceptibility and the Fe_d content (R² = 0.683) and Fe_d/Fe_t ratio (R² = 0.780) in soils, indicating that pedogenic SP ferrimagnetic grains were associated with enrichment of the secondary iron oxide minerals in the weathering process of soil. Rock magnetism analysis showed that the major magnetic carriers in the weakly weathered soil profiles are magnetite and/or maghemite, and the highly developed soil profiles are generally enriched in magnetite/maghemite grains of pedogenic origin and the magnetically hard haematite, indicating that the magnetic component was transformed from a ferrimagnetic phase (magnetite) to antiferromagnetic phase (hematite) during pedogenic development. Results indicated that some of the magnetic parameters of soils, in this case χfd, can be useful for pedogenic comparisons and age correlations in the weathering sequence of soil. It is thus suggested that multiparameter rock magnetic investigations represent a more powerful approach for pedogenesis.     

Nature of redox concentrations in a sequence of agriculturally developed acid sulfate soils in Thailand

Potential acid sulfate soils (PASS) are drained for agriculture, resulting in the formation of active acid sulfate soils (AASS), which gradually evolve into post-active acid sulfate soils (PAASS). Various redox concentrations (precipitates, costings, and mottles) occur in these soils as a result of pedogenic processes including biological activity and effects of land management. Although several studies have determined the mineralogy and geochemistry of ASS, the mineralogy and geochemistry of redox concentrations occurring in a sequence of ASS through PASS to PAASS have not been investigated. This study examined the mineralogy and geochemistry of redox concentrations and matrices within 5 PASS, 8 AASS, and 5 PAASS in Thailand. The labile minerals were predominantly controlled by oxidation status and management inputs. The unoxidized layers of PASS, AASS, and PAASS contained pyrite and mackinawite. The oxidation of Fe sulfides caused acidification and accumulation of yellow redox concentrations of jarosite and Fe (hydr)oxides at shallow depths. As the soils became well developed, they were recognized as PAASS, and the jarosite and goethite transformed to hematite. As ASS were drained, Co, Mn, Ni, and Zn moved downward and were associated with Fe sulfides and Mn oxides in the unoxided layer. Concentrations of As, Cu, Cr, Fe, and V did not change with depth because these elements became associated with jarosite and Fe (hydr)oxides in yellow and red redox concentrations, as well as the root zone, in the partly oxidized layer of AASS and PAASS. Arsenic was associated with pyrite under reducing conditions.     

海南砖红壤的微形态特征以及南方网纹红土与砖红壤环境意义的差异

主要运用土壤微形态学、粘土矿物学和土壤化学方法,对海南岛三个不同母质的砖红壤剖面的微形态特征和成壤过程进行研究,并将网纹红土和砖红壤进行比较.结果表明,砖红壤典型的微形态特征为易风化矿物颗粒和粘粒胶膜的缺失、均质状的b-垒结以及风化成因铁锰质结核的出现;典型的成壤过程为强烈的化学风化、红化、均质化、淋溶以及显著的脱硅富铝化过程.随着成土母质和土壤排水条件的变化,砖红壤的微形态特征亦有所差异.而我国南方的网纹红土的发育程度低于砖红壤,不宜被划分为砖红壤或氧化土,而更趋向归入老成土,在我国土壤发生学分类中大致相当于红壤.     

The origin of carbonates in termite mounds of the Lubumbashi area, D.R. Congo

The origin of carbonate accumulations in termite mounds is a controversial issue. This study is an attempt to elucidate the processes of carbonate precipitation in Macrotermes mounds built on Ferralsols in Upper Katanga, D.R. Congo, whereby a differentiation between pedogenic and inherited carbonates is considered. Carbonate features were investigated for a 9 m deep termite-mound profile, and for an 18 m wide cross-section through a termite mound and the adjacent soil, using field and laboratory techniques. Field evidence for a pedogenic origin includes morphological type (soft powdery materials, nodules, and coatings on ped surfaces) and distribution patterns of the carbonates. Thin-section studies reveal that the carbonates occur predominantly as impregnative orthic nodules and less commonly as coatings, both clearly pedogenic; calcareous pellets are interpreted as locally reworked pedogenic carbonates. X-ray diffraction (XRD), scanning electron microscopy/energy dispersive X-ray spectrometry (SEM-EDS) and stable isotope (δ¹³C) analyses show that all isolated carbonate features consist of high-Mg calcite (4.9-12.3 mol% MgCO₃) with δ¹³C signatures ranging from − 13.2‰ to − 11.5‰. Weddellite (CaC₂O₄. 2H₂O) is identified in a thin-section and by XRD analysis, and appears to be locally transformed into calcite. The stable isotope composition of carbon suggests that calcite precipitated in equilibrium with soil CO₂ generated during decomposition of soil organic matter, and locally most likely during oxidation of oxalate. This study proves that carbonates which accumulated in Macrotermes mounds are pedogenic precipitates, whose deposition is partly related to microbial decay of organic matter, subsequently redistributed to some extent by abiotic dissolution-reprecipitation and termite activity.     

Distribution of total and extractable forms of iron,manganese, and aluminum in development of rice soils of saga polder lands

The distribution of pedogenic oxides of Fe, Mn, and Al was described for rice soils of Saga polder lands and its relationship to soil development with time was investigated. The distribution of Mn largely parallelled that of Fe and in response to the soil development their accumulation occurred in the B horizons of the profiles. Manganese was the clement most susceptible to downward movement, which lad to a pronounced lowering of extractable Mn content in the surface horizons in well-developed soil morphology. By contrast, this is not the case for Al which, in general, had little change in extractable Al and a slight increase in total Al with depth as the time increased. Apparently the distribution of Mn was largely governed by the extent of reduction processes, whereas in the Al distribution clay migration may be a principal controlling factor. The distribution of Fe may be due chiefly to the reduction processes, with some contribution from the clay migration.     

Transformations of layered silicates in soils of the boreal and subboreal zones: Literature review

The transformation mechanisms of layered silicates during the formation of vermiculite (vermiculitization), smectite (smectization), illite-like minerals (illitization), and soil chlorites (chloritization) have been considered. The mechanism of olivization has also been discussed. The manifestation features of these processes in different soils and horizons have been analyzed. It has been shown that the rate, direction, and depth of the transformations depend on the climatic conditions; the mineral composition; the acid-base, redox, and hydrological conditions; and the soil solution’s composition. The amount of the accumulated solid-phase products of the transformations depends on the rate of the given transformation stage and (or) the rate ratio between the given and the next transformation stages.     

Review on iron availability in soil: interaction of Fe minerals,plants, and microbes

Purpose

The rationale of this paper is to review the state of the art regarding the biotic and abiotic reactions that can influence Fe availability in soils. In soil, the management-induced change from oxic to anoxic environment results in temporal and spatial variations of redox reactions, which, in turn, affect the Fe dynamics and Fe mineral constituents. Measuring the Fe forms in organic complexes and the interaction between bacteria and Fe is a major challenge in getting a better quantitative understanding of the dynamics of Fe in complex soil ecosystems.

Materials and methods

We review the existing literature on chemical and biochemical processes in soils related with the availability of Fe that influences plant nutrition. We describe Fe acquisition by plant and bacteria, and the different Fe–organic complexes in order to understand their relationships and the role of Fe in the soil carbon cycle.

Results and discussion

Although total Fe is generally high in soil, the magnitude of its available fraction is generally very low and is governed by very low solubility of Fe oxides. Plants and microorganisms can have different strategies in order to improve Fe uptake including the release of organic molecules and metabolites able to form complexes with Fe^III. Microorganisms appear to be highly competitive for Fe compared with plant roots. Crystalline Fe and poorly crystalline (hydro)oxides are also able to influence the carbon storage in soil.

Conclusion

The solubility of crystalline Fe minerals in soil is usually very low; however, the interaction with plant, microbes, and organic substance can improve the formation of soluble Fe^III complexes and increase the availability of Fe for plant growth. Microbes release siderophores and plant exudates (e.g., phytosiderophores, organic acids, and flavonoids), which can bind and solubilize the Fe present in minerals. The improved understanding of this topic can enable the identification of effective solutions for remedying Fe deficiency or, alternatively, restricting the onset of its symptoms and yield’s limitations in crops. Therefore, development and testing of new analytical techniques and an integrated approach between soil biology and soil chemistry are important prerequisites.     

MAGNETIC SUSCEPTIBILITY OF THE SOIL AND ITS SIGNIFICANCE IN SOIL SCIENCE – A REVIEW

The magnetic susceptibility of soil minerals is discussed, and in particular that of the ferrimagnetic minerals, maghemite, magnetite, and the titanomagnetites since one or more of these usually dominates soil magnetic properties. The magnetic susceptibility of soil depends on the shape, size, and concentration of these minerals as well as on the method of measurement. Measurements performed in a weak alternating magnetic field are the most reliable. The identification, formation, and occurrence of soil maghemite is considered in detail since it is usually of pedogenic origin and occurs in (magnetically) detectable amounts in most soils. Moderate concentrations (>1 per cent) of magnetite or titanomagnetite in soils may be accurately measured if some of the material is first magnetically separated and its susceptibility determined. An example is given of the use of susceptibility measurements. Pedogenic maghemite may be determined in soils developed from parent materials of low susceptibility. A very rough value of 8.8 × 10^?4 m³ kg^?1 is suggested for the mass susceptibility of such maghemite (excluding magnetic concretions). Although susceptibility has been suggested as an indicator of soil forming processes, this is only possible within an area containing fairly uniform parent material.